Gaseous fuel powered engines are common in locomotive applications. For example, the engines of a locomotive can be powered by natural gas alone or by a mixture of natural gas and diesel fuel. A preferred form of natural gas for transport with locomotives is liquid natural gas (LNG) because of its higher energy density. Natural gas may be condensed into liquid form by cooling it to approximately −162° C. (−260° F.), and then stored in refrigerated or pressurized vessels or tanks The liquid natural gas can then later be converted into a gaseous state by heating it before it is delivered to the locomotive engines.
As demands for reduced emissions and increased efficiency grow, it is becoming preferred that the natural gas be delivered to the engine at higher and higher pressures (i.e., high pressure direct injection). Converting and pressurizing natural gas to the desired pressure can be accomplished by a gas compressor, a linear piston pump, or other high-pressure pump. However, these methods produce unacceptable parasitic losses to the overall engine power efficiency (either in magnitude or quality), diminishing the economic viability of natural gas as a fuel source. Therefore, an energy efficient method of converting and pressurizing the natural gas is desired.
One method of trying to convert and pressurize liquid fuel to a compressed gaseous fuel for delivery to an engine is described in U.S. Pat. No. 5,375,580 (“the '580 patent”) issued to Stolz et. al. on Dec. 27, 1994. The '580 patent describes a locomotive fueled by a refrigerated liquid fuel that is converted and pressurized using a high-pressure pump and a vaporizer connected in series.
Although the method of the '580 patent may be capable of converting and pressurizing a refrigerated liquid fuel to a pressurized gaseous fuel, it may still be less than optimal. Specifically, operation of the high-pressure pump described in the '580 patent may produce substantial parasitic losses. Consequently, both the energy efficiency of the locomotive and the advantages of utilizing natural gas may be diminished.
The disclosed fuel system is directed to overcoming one or more of the problems set forth above and/or other problems with existing technologies.